WASHINGTON — The Supreme Court on Monday put restrictions on companies that want to clean up voluntarily their polluted land and sue former owners to share the costs.

The court ruled 7-2 against a company that in 1981 bought land in Texas that had been used for aircraft engine maintenance businesses and then went to court to recover some of the $5 million it spent cleaning up pollution there.

The justices said the company improperly tried to use the Superfund law to sue because the government had not demanded that the cleanup be done.

However, the court left open the possibility that another part of the Superfund law could permit such lawsuits.

"There's no question this ruling will significantly diminish the incentive people have to do voluntary cleanup," said Richard Lazarus, a Georgetown University law school professor and environmental lawyer.

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Congress may be asked to change the law, Lazarus said.

The law allows the Environmental Protection Agency to designate as "Superfund" sites areas that are highly polluted, and then officials can seek money from current and former owners for the cleanup costs.

Monday's case involved a broad category of land, many thousands of properties, that have abandoned toxic plants, landfills and mines but are not a priority for the EPA.

Justice Clarence Thomas, writing for the court, said that lower courts should reconsider whether to allow the lawsuit by Aviall Services Inc. against electrical product maker Cooper Industries.

In a dissent, Justices Ruth Bader Ginsburg and John Paul Stevens said the Supreme Court should have settled the issue now, and let Aviall pursue help.

During the argument in the case in October, Ginsburg appeared troubled about preventing lawsuits until the government gets involved and demands property cleaning.

"You might be sitting around waiting forever until EPA comes after you," she said then. "It seems like EPA has higher priorities."

The Bush administration had urged the court to limit the use of the law. But 23 states argued that the Superfund law, passed in 1980, allows lawsuits when companies on their own initiative seek to clean properties. Those efforts often are very expensive and can involve multiple former owners.